How many deck boards do I need?

Enter your deck width and length, board width, and spacing. The calculator divides the deck area by board coverage, rounds up to whole boards, and adds joist, post, concrete tube form, and fastener counts.

What materials do I need to build a deck or fence?

The estimator builds a bill of materials: surface boards or fence pickets, joists or rails, posts, concrete tube forms, and fasteners. Enter your dimensions, joist or rail spacing, and post spacing to get the full list.

How do I estimate deck or fence material cost?

Enter your dimensions and board size, then set a cost per board and per post. The calculator multiplies board count plus framing and fastener quantities by your input prices and shows the total estimated material cost.

Outdoor

Deck / Fence Material Estimator

Build a practical material list with deck boards, joists, posts, tube forms, fasteners, and estimated cost.

Use this free online Deck Calculator to turn a rough deck idea into a practical material estimate. Enter your deck length, width, board size, board gap, and joist spacing, then get quick numbers for square footage, decking needs, joists, and waste so you can plan smarter before buying materials.

How it works

The calculator starts with the basic deck area formula: length x width = total square feet. For decking, it converts your board face width plus the gap into feet, then estimates decking as deck area divided by board coverage. If you’re using full-length boards, divide the total linear feet by board length to estimate board count. For framing, joists are estimated with: deck length divided by joist spacing, then plus 1. At 16 in OC, spacing is 16 ÷ 12 = 1.333 ft. Finally, add 10% waste for cuts, angled ends, layout changes, and damaged boards. Always round up, because you can’t buy part of a board or joist.

Worked examples

A 12 x 16 ft deck = 12 x 16 = 192 sq ft. With 5.5 in boards plus a 0.25 in gap, coverage = 5.75 in ÷ 12 = 0.479 ft. Decking needed = 192 ÷ 0.479 = 400.8 linear ft. Using 16 ft boards: 400.8 ÷ 16 = 25.1 boards. Add 10% waste: 25.1 x 1.10 = 27.6, so buy 28 boards. Joists at 16 in OC: 16 ÷ 1.333 + 1 = 13 joists.
A 10 x 20 ft deck = 10 x 20 = 200 sq ft. With 5.5 in boards plus a 0.25 in gap, coverage = 5.75 in ÷ 12 = 0.479 ft. Decking needed = 200 ÷ 0.479 = 417.5 linear ft. Using 20 ft boards: 417.5 ÷ 20 = 20.9 boards. Add 10% waste: 20.9 x 1.10 = 23.0, so buy 23 boards. Joists at 16 in OC: 20 ÷ 1.333 + 1 = 16 joists.
A 14 x 18 ft deck = 14 x 18 = 252 sq ft. With 5.5 in boards plus a 0.25 in gap, coverage = 5.75 in ÷ 12 = 0.479 ft. Decking needed = 252 ÷ 0.479 = 526.1 linear ft. Using 18 ft boards: 526.1 ÷ 18 = 29.2 boards. Add 10% waste: 29.2 x 1.10 = 32.1, so buy 33 boards. Joists at 16 in OC: 18 ÷ 1.333 + 1 = 14.5, so use 15 joists.

FAQ

How do I calculate deck square footage?

Multiply deck length by deck width. A rectangular deck that is 12 ft long and 16 ft wide has an area of 12 x 16 = 192 sq ft.

Why does board gap matter?

The gap changes the coverage of each deck board row. A 5.5 in board with a 0.25 in gap covers 5.75 in total, which affects the linear feet of decking needed.

How is joist count estimated?

Use deck length divided by joist spacing, then add 1. For 16 in OC spacing, convert 16 in to 1.333 ft before calculating, then round up to a whole joist.

Should I add waste to my deck material estimate?

Yes. Adding 10% waste helps cover cuts, trimming, mistakes, damaged pieces, and layout changes. It’s better to round up before ordering than to run short mid-build.